Motor control system



Aprll 27, 1937. B. o. AUSTIN ET AL MOTOR CONTROL SYSTEM Filed Jan. 2,` 1955 m i a E n shv mNT wmqm Nn Fs E mm ,TS m a. mmv. Se mmm/U o mm SWX l nwm A 5 mmv m mm m61 n C \m 01111' 5 E Num www w @m w f mE W55 Nw E. j SYN E \& 4 V T i@ I l i l i l l NS a; Nm Q QN wm mm wm /R S mw r uw Patented Apr. 27, 1937 2,078,216

UNITED STATES PATENT OFFICE MOTOR CONTROL SYSTEM Bascum O. Austin, Forest Hills, and Norman H. Willby, Irwin, Pa., assignors to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application January 2, 1935, Serial No. 68v

7 Claims. (Cl. 172-288) O-ur invention relates, generally, to motor conconjunction with the accompanying drawing, in trol systems, and, more particularly, to systems which:

for controlling the operation of the propelling Figure 1 is a diagrammatic view of a motor motors of electric Vehicles, such as street cars control system embodying our invention; and 5 and trackless-trolley coaches. Fig. 2 is a chart showing the sequence of op- 5 An object of our invention, generally stated, eration of certain of the switches illustrated in is to provide a motor control system which shall Fig. 1.

be simple and eicient in operation, and which Referring now to the drawing, the system may be economically manufactured and inshown comprises a pair of electric motors IU l stalled. and Il, which may be of any type suitable for 10 A more specic object of our invention is to propelling a trolley bus or other electricallyprovide an automatic accelerating system in propelled vehicle. The motors shown are of the which the shunting of more than one step of reseries type, the motor l having an armature sistance at a time during the automatic progres- Winding i2 and a series eld winding I3, and the l5 sion of the control system is definitely premotor H having an armature winding I4 and 15 vented. a series eld winding l5. Electrically operated Another object of our invention is to provide switches i6 and Il are provided for connecting an automatic accelerating system having varithe motors i5 and li to current collecting deable rates of acceleration for the propelling movices I8 and I9, which engage overhead power tors of an electric vehicle. conductors 2l and 22, respectively. A plurality D Still another object of our invention is to proof resistors 23, 24 and 25 are provided for convide a motor control system in which step-loytrolling the motor current during the accelerastep acceleration can be obtained as well as tion of the motors and electrically operated automatic acceleration of the motors. switches 2B, 21 and 2S are provided for shunt- A still further object of our invention is to ing the resistors 23, 24 and 25, respectively. prevent the progression of an automatic control In addition to the foregoing resistors, a resistor system during dynamic braking of the motors 29 is utilized during dynamic braking of the until the motor voltage has attained a predetermotors to control the motor current, and elecmined Value. trcally operated switches 3| and 32 are pro- 30 Other objects of our invention will be exvided for establishing the dynamic braking conplained fully hereinafter or will be apparent nections for the motors.. A master controller 33, 30 to those skilled in the art. which may be oi the drum type, is provided In accordance with one embodiment of our for controlling the motors while they are proinvention, the progression of an automatic conpelling the vehicle and a similar controller 34 35 trol system is governed by a plurality of limit is utilized during dynamic braking. The two V relays, one of which may be provided for each controllers are so electrically interlocked that o step of the control system. The limit relays are it is necessary for the accelerating controller so connected in the system that they are succes- 3,3 to be inthe off position before the controller sively energized as the accelerating switches are 34 can be effective in establishing the braking 40 closed and each switch in the progression canconnections. 40

not close until the motor current is of such a In order that the acceleration, and also the value that its respective limit relay operates to dynamic braking of the vehicle, may be autoenergize the Switch. Dorine' dynamic braking, matically controlled, as Well as manually by the same resistors and switches are utilized to means of the controllers 33 and 34, current limit 60'1'1151'01 the mOOI' Current 2S during accelerarelays 35 and 36 are provided for automatically 4. tion, but the automatic progression is prevented controlling the operation of the resistor shuntfrom starting until the motor voltage has built ing or accelerating switches 21 and 28 as will up to a predetermined value. Variable rates of be more fully described hereinafter. acceleration and braking are obtained by loro- With a view to preventing the skipping of so Vidrlg atllatng COllS 011 the limit relays haV- notches or steps and to ensuring that the motor llg a plurality 0f taps WlliCh are gOVerIled by current has dropped to the proper value before the ole-Stel oootrolleradditional resistance is snunted from the motor For a fuller understanding of the nature and circuit, a limit relay is provided for each step objects oi our invention, reference may be had in the automatic progression and each limit to the following detailed description, taken in relay controls only one of the accelerating 55 switches, instead of one limit relay controlling all of the switches, as in previously known systems. The limit relays are so connected in the motor circuit that they are successively energized by the motor current as each step of resistance is shunted from the motor circuit by the accelerating switches. The next switch in the progression cannot .operate until permitted to do so by the limit relay that was energized by the closing of the preceding switch.

As shown, each current limit relay is provided with two coils which are disposed on the relay in opposed relation. In this instance a series coil pulls down on the relay armature and a shunt coil pulls up. When neither coil is energized, the relay is actuated by gravity to its lowermost position, in which position the contact members of the relay are open and they can be closed only by the shunt coil raising the relay armature. Since the series coil is energized by the motor current in the foregoing manner and the shunt coil is energized by the trolley potential, it will be seen that the relay cannot close until the motor current falls to a value which will permit the shunt coil to overcome the series coil. Thus, the next switch in the progression cannot operate until the motor current has dropped to a predetermined value. In order that variable rates of acceleration, and also dynamic braking, may be obtained, the shunt coils on the limit relays may be provided with one or more taps, the connections to which are controlled by the master controller. In this manner, the maximum rate of acceleration may be obtained by energizing the entire shunt coil windings, or a lower rate may be obtained by energizing only a portion of the windings through their respective taps.

In order to insure that the voltage of the machines I0 and II will build up quickly when dynamic braking connections are established, the ileld winding I5 of the motor I I is connected to the power source through a resistor 31 during the first part of the braking cycle. After the voltage of the machines has once built up, it is no longer necessary to separately excite the field winding of the one machine.

With a view topreventing the resistor shunting switches from being automatically operated before the voltage of the machines I0 and II has built up, when the dynamic braking connections are established, a relay 38 is connected across the machines I0 and II to be responsive to the voltage of the machines. The contact members of the relay 38 are so connected in the control system that the operation of the resistor shunting switches cannot take place until the voltage of the machines IIJ and II has been built up to a predetermined value. However, the relay 38 is elfective only during dynamic braking and not during acceleration of the motors.

With a view to simplifying the drawing and the description of the control system, only a few steps of resistance have been shown in the motor circuit. It will be understood that additional resistors, accelerating switches and limit relays may be readily provided, if desired.

In order that the functioning of the foregoing apparatus may be more clearly understood, the operation of the system will now be described. Assuming that it is desired to accelerate the vehicle under manual control of the operator, the master controller 33 may be actuated to position I, thereby energizing the actuating coils of the line switches I6 and I1, which causes the motors 60 and II to be connected to the current collectors I8 and I9. The energizing circuit for the coil of the line switch I1 may be traced from the positive power conductor 2I through the current collector I8, conductor 4|, contact iingers 42 and 43, bridged by a contact segment 44 on the controller 33, conductors 45 and 46, the actuating coil 41 on the line switch I1, conductors 48 and 49, and the current collector I9 to the negative power conductor 22. The circuit through the actuating coil of the line switch I6 extends from the previously energized conductor 46 through the actuating coil 5I, conductor 52, an interlock 53 on the switch 3|, conductor 54, an interlock 55 on the switch I1 and conductor 48 to the negative conductor 49.

The motors I0 and II are now connected to the power source in parallel-circuit relation. The circuit through the motor I0 may be traced from the positive conductor 2I through the current collector I8, conductors 4I and 51, contact members 58 on the switch I6, conductor 59, the resistors 23, 24 and 25, conductor 6I, contact members 62 on the switch I6, conductor 63, the eld winding I3 and armature winding I2 of the motor I0, conductors 64 and 65, contact members 66 on the switch I1, conductor 61 and the current collector I9 to the negative conductor 22. The circuit through the motor II extends from the previously energized conductor 63 through conductor 68, the armature winding I4 and the eld winding I5 of the motor II to the conductor 65, and thence through the circuit previously traced to the negative conductor 22.

Since the motors I0 and II are connected in series with the resistors 23, 24 and 25, they will rotate at a low speed. The motors may be accelerated in a manner well known in the art by moving the controller 33 to position 2, thereby closing the accelerating switch 26 to shunt the resistor 23 from the motor circuit. The energizing circuit for the actuating coil of the switch 26 may be traced from a contact linger 1I which engages the segment 44, conductor 12, the actuating coil 13 on the switch 26, and conductor 14 to the negative conductor 49. When the switch 26 is actuated to its uppermost position, the contact members 15 are closed to shunt the resistor 23 from the motor circuit.

It will be noted that the series coil 16 of the limit relay 35 is connected in the motor circuit when the resistor shunting switch 26 is closed. Therefore, the series coil 16 is energized by the motor current. The operation of the switch 26 also completes the energizing circuit for a portion of the winding of the shunt coil of the limit relay 35. The energizing circuit for the shunt coil may be traced from a contact finger 11, which engages the segment 44 on the controller 33, conductors 18, 19 and 8l, the lower portion 82 of the winding of the shunt coil on the relay 35, conductors 83 and 84, an interlock 85 on the switch 26, and conductor 86 to the negative conductor 49.

As explained hereinbefore, the limit relay 35 will be raised to its uppermost position when the motor current is reduced to a value which will permit the shunt winding 82 on the limit relay to overcome the force exerted by the series windings 16, thereby permitting the next step of acceleration to be taken.

Assuming that the limit relay 35 is raised to its uppermost position, the actuating coil of the switch 21 may be energized to close this switch by moving the controller 33 to position 3. The energizing circuit for the actuating coil of the dynamic braking connections are first established, thereby insuring that the voltage of the machines I and II will build up quickly and dynamic braking take eiect immediately. The circuit providing separate excitation for the eld winding I may be traced from the power conductor 2|, through the current collector I8, conductors 4|, 51 and |31, resistor 31, contact members |38 on the switch 32, conductor |36, the field winding I5, conductor 65, the contact members 66 on the switch I1, conductor 61 and the current collector I9 to the negative power conductor 22. By separately exciting the field winding I5, it is insured that the motor II will immediately start generating current, thereby providing excitation for the field winding I3 of the motor I0, which will also function as a generator.

The current generated by the machines I0 and I I, and therefore, the braking effect of these machines may be controlled by means of the resistors 23, 24 and 25 and their respective shunting switches, 26, 21 and 28, in a manner similar to that utilized during the acceleration of the motors I0 and II, by closing the switches 26, 21 and 28 in sequential relation to shunt the resistors 23, 24 and 25 from the motor circuit.

However, as explained hereinbefore, the closing of the switch 26 which is the first one in the progression, cannot take effect until the voltage of the machines I0 and II has built up to a predetermined value to operate the relay 38, which controls the energization of the actuating coil of the switch 26. Assuming that the voltage of the machines I0 and II has reached a value which will cause the relay 36 to close its contact members, the switch 26 may be operated to shunt the resistor 23, by actuating the controller 34 to position 2, thereby energizing the actuating coil of the switch 26. The circuit through the coil of this switch may be traced from a contact finger I4I, which engages the segment I9, through conductor |42, the contact members |43 on the relay 36, conductor 12, the actuating coil 13 of the switch 26 and conductor 14 to the negative conductor 49.

The switches 21 and 28 may be closed in sequential relation by either actuating the controller 34 to positions 3 and 4 in a step-by-step manner, under manual control of the operator, or by actuating the controller 34 to position 5, which will cause the switches 21 and 28 to be automatically closed under the control of the limit relays 35 and 36 in the same manner as during the acceleration of the motors IIJ and II. In either event, the switch 21 cannot be closed until the motor current has been reduced to a value which will permit the limit relay 35 to be operated to close its contact members after the switch 26 has been closed, and the switch 28 cannot be operated until the limit relay 36 has closed its contact members after the switch 21 has been closed.

In this manner, the rate of deceleration of the vehicle by dynamic braking is controlled by the limit relays 35 and 36 in the same manner as the rate of acceleration is controlled. If the maximum rate of deceleration is desired, the controller 34 may be actuated to position 6, thereby energizing the entire shunt windings on the limit relays 35 and 36 and deenergizing the contact finger 18, which will cause the relays to operate at a higher value of motor current, as explained hereinbefore.

Since it is not necessary to provide separate excitation for the field winding I5 of the motor II after the voltage of the motors I0 and II has been built up, the switches 32 and I1 are permitted to open when the controller 34 is actuated to position 3, thereby interrupting the exciting circuit after the dynamic braking is established. The resistor 29 is not shunted from the motor circuit during dynamic braking, in order that the dynamic braking effect will be gradually reduced as the speed of the vehicle is decreased.

From the foregoing description, it is apparent that we have provided a control system which is both simple and flexible in operation, since it is possible to obtain step-by-step acceleration under the control of a vehicle operator or automatic acceleration at variable rates. By providing a separate limit relay for each step of acceleration, each notch is definitely tested, to make sure that the motor current has dropped to the proper value, before the next step in the progression can be taken, thereby preventing overloading of the motors. Skipping of notches during automatic acceleration is definitely prevented by the action of the limit relays. Furthermore, the progression is obtained in a denite sequence since it is impossible to operate any one of the accelerating switches until the preceding switches have been operated.

We do not desire to be restricted to the specie embodiment of the invention herein shown and described, since it is evident that it may be changed and modified without departing from the spirit and scope of the invention, as dened in the appended claims.

We claim as our invention:

1. In a motor control system, in combination, a motor, a source of power for the motor, switching means for connecting the motor to the power source, a, controller for controlling the operation of said switching means, a plurality of resistors for controlling the motor current, a plurality of switches for shunting the resistors step-by-step, a plurality of current limit relays cooperating with the controller to control the operation of said resistor shunting switches, each of said relays having a coil energized by the motor current in sequential relation as the resistor shunting switches are operated, and means on said relays associated with said controller for changing the operating characteristics of the relays.

2. In a motor control system, in combination,

a motor, a source of power for the motor, switching means for connecting the motor to the power source, a controller for controlling the operation of said switching means, a plurality7 of resistors for controlling the motor current, .a plurality of switches for shunting the resistors step-by-step, and a plurality of current limit relays cooperating with the controller` to control the operation of said resistor shunting switches, each of said rela-ys having a series coil energized by the motor current and a shunt coil energized from the source of power as the resistor shunting switches are operated in sequential relation.

3. In a motor control system, in combination, a motor, a source of power for the motor, switching means for connecting the motor to the power source, a controller for controlling the operation of said switching means, a plurality of resistors for controlling the motor current, a plurality of switches for shunting the resistors in sequential relation, the first one of said switches being controlled by the controller, limit relays responsive to the motor current and cooperating with the controller to control the remaining switches, each limit relay controlling only one of said switches,

and means on said relays associated with said controller for changing the operating characteristics of the relays.

4. In a motor control system, in combination, a motor, a source of power for the motor, switching means for connecting the motor to the power source, a controller for controlling the operation of said switching means, a plurality of resistors for controlling the motor current, a plurality of switches for shunting the resistors in sequential relation, a plurality of current limit relays responsive to the motor current and cooperating with the controller to control the operation of the resistor shunting switches, interlocking means l5 on said switches for controlling the energization of the current limit relays, and means on said relays energized through said controller for governing their operation.

5. In a motor control system, in combination, a motor, a source of power for the motor, switching means for connecting the motor to the power source, a controller for controlling the operation of said switching means, a plurality of resistors for controlling the motor current, a plurality of switches for shunting the resistors in sequential relation, a plurality of current limit relays cooperating with the controller to control the operation of the resistor shunting switches, each of said relays having a series coil energized by the motor current and a separately energized shunt coil, and means operated by the resistor shunting switches for controlling the energization of the series coils and the shunt coils on the limit relays.

6. In a motor control system, in combination, a motor, a source of power for the motor, switching means for connecting the motor to the power source, a controller for controlling the operation of said switching means, a plurality of resistors for controlling the motor current, a plurality of switches for shunting the resistors in sequential relation, and a plurality of current limit relays cooperating with the controller to control the operation of the resistor shunting switches, each of said relays having a series coil energized by the motor current and a separately energized shunt coil provided with a plurality of taps and disposed to oppose the series coil.

7. In a motor control system, in combination, a motor, a source of power for the motor, switching means for connecting the motor to the power source, a controller for controlling the operation of said switching means, a plurality of resistors for controlling the motor current, a plurality of switches for shunting the resistors in sequential relation, and a plurality of current limit relays cooperating with the controller to control the operation of the resistor shunting switches, each of Said relays having a series coil energized by the motor current and a separately energized shunt coil provided with a plurality of taps and disposed to oppose the series coil, .and means on the controller for governing the energization of the shunt coils to vary the rate of acceleration of the motors.

BASCUM O. AUSTIN. NORMAN H. WILLBY. 

